As Maureen Doyle pointed out, you can source magnesium formate from a
company in the USA called Pfaltz & Bauer. Try to fax them and ask
if they have a UK office:
USA Fax Number: 203 574 3181
Magnesium formate, Pfaltz & Bauer catalog number M00340 $52.00 for 200g
Good luck, let us know if you need anything else.
Sincerely, Bob Cudney - Hampton Research (xtalrox at aol.com)